Feather-based biomarkers link geography, physiology and reproduction across the annual cycle in northern pintails

Conditions that individuals experience during the nonbreeding season can have subsequent effects on breeding performance (i.e. carry-over effect), with implications for population dynamics. We used feather biomarkers from breeding female northern pintails (Anas acuta) to evaluate whether body condition and timing of nest initiation were related to prior moult and nonbreeding locations as estimated by both band recoveries and stable isotopes (δ2H, δ15N, δ13C, δ34S). We then assessed if relative energetic load as indexed by feather corticosterone (CORTf) incorporated into feathers prior to breeding influenced individual condition and timing of nesting. Body condition of nesting pintails was unrelated to isotope-predicted nonbreeding region, CORTf values, or nesting date. However, later-nesting females had higher levels of CORTf in body feathers grown on nonbreeding areas or during pre-breeding migration and, overall, females using nonbreeding habitats near coastal areas had later nest initiation dates compared to those occupying inland nonbreeding habitats. Reduced frequency or severity of energetic challenges during nonbreeding seasons due to enhanced foraging opportunities may facilitate earlier onset of egg-laying by breeding females.